I created a Start File; When used, though, the materials are broken
Pink means that something was either moved, or is now missing.
The first thing to do is to run File&gt;External Data&gt;Report Missing Files* and File&gt;External Data&gt;Find Missing Files to report and locate the missing files.
Note from the manual:

Report Missing Files
This option is useful to check if there are links
to unpacked files that no longer exist. After selecting this option, a
warning message will appear in the Info editor’s header. If no warning
is shown, there are no missing external files.
Find Missing Files
In case you have broken links in a blend-file, this option will help you to fix the problem. A File Browser will show up. Select the
desired directory (or a file within that directory), and a search will
be performed in it, recursively in all contained directories. Every
missing file found in the search will be recovered. Those recoveries
will be done as absolute paths, so if you want to have relative paths
you will need to select Make All Paths Relative.

Once you have fixed your file paths, save your start-up file again with Ctrl+U